could just be stress 1st time dealing with this . I know my males get worked up and usually lose there appetite when the girls are in heat. I would stick with the pumpkin and if wanted you could add some probiotics to his food as well , just a small amount.
she is new to the home? has she been vet checked at all? dewormed? has he been dewormed regular?no change in diet? Best guess would be stress but really could be a hundred reasons why a dog can come down with diarreah.
While he is like this watch his fluid intake, you don't want him getting dehydrated if it is severe so just make sure he is drinking enough, could add pedyalite to help with the electrolytes or chicken broth .
Pit bulls are..... Beauty without Vanity, Strength without Insolence, Courage without Ferocity, and all the Virtues of Man, without his Vices.""